LED lighting assemblies with thermal overmolding

ABSTRACT

One or more light emitting diode diodes (LEDs) are attached to a printed circuit board. The attached LEDs are connectable with a power source via circuitry of the printed circuit board. An overmolding material is insert molded an over at least portions of the printed circuit board proximate to the LEDs to form a free standing high thermal conductivity material overmolding that covers at least portions of the printed circuit board proximate to the LEDs. The free standing high thermal conductivity material has a melting temperature greater than about 100° C. and has a thermal conductivity greater than or about 1 W/m·K. In some embodiments, the free standing high thermal conductivity material is a thermoplastic material.

BACKGROUND

The following relates to the lighting arts. It especially relates toLED-based lighting assemblies including LED-based lighting assemblymodules for flexible lighting strips. However, the following will alsofind application in conjunction with lighting assemblies, methods formanufacturing lighting assemblies, electronics associated with lightingassemblies, and applications employing lighting assemblies, such asillumination, illuminated channel lettering, border lighting, and soforth.

Light emitting diodes (LEDs) are used in lighting assemblies, where theyhave certain advantages of incandescent, fluorescent, and other lightingtechnologies. For example, LEDs are compact, durable, relatively energyefficient, operable at low voltage, and so forth. In a typicalarrangement, one or more LEDs are attached to a printed circuit boardand are connectable with a power source via circuitry of the printedcircuit board. If the power source is not directly compatible with theLEDs (for example, a 110 VAC house voltage applied to LEDs thattypically operate at a few volts DC) then the printed circuit can alsoinclude power conditioning circuitry that converts the power to a formamenable to driving the LEDs. Alternatively or additionally, an AC/DCconverter, DC power supply, or other power conditioning component can beinterposed between the 110 VAC and the printed circuit board.

High brightness LEDs in lighting assemblies typically operate atrelatively low voltage but relatively high current. The total electricalpower input to a commercial high-brightness LEDs is typically at thelevel of hundreds of milliwatts to a few watts per LED. Accordingly,efficient removal of generated heat is a concern.

One known approach for removing excess heat generated during LEDoperation is the use of metal heat sinks. Luxeon® LED emitters(available from LumiLeds Lighting, LLC, San Jose, Calif.) and some othercommercial high-brightness LEDs include a metal heat slug on which thesemiconductor chip is attached or otherwise thermally contacts. In orderto maintain a compact profile, the metal heat slug of the LED cannot bevery large, and is typically intended to conduct heat to a largerexternal heat sink that provides dissipation of heat to the surroundingambient. Accordingly, the LED is mounted on a metal heat sink. In somelighting assemblies, the metal heat sink is incorporated into theprinted circuit board. Such a composite board is commonly referred to asa metal core printed circuit board.

A metal heat sink adds substantial cost and weight to the lightingassembly, and may be relatively inefficient at dissipating heat. Commonheat sink metals such as copper have high density, making heat sinksmassive. Moreover, the surface area for dissipation of heat to theambient corresponds to the surface area of the metal heat sink. Toachieve good thermal coupling with the ambient, metal heat sinkstypically include fins or other radiating structures, which increasesweight and bulk of the heat sink. Optionally, forced air convectiongenerated by a fan can be used to increase heat transfer to the ambient,or active water cooling can be incorporated. However, these approachesadd substantial cost, bulk, and complexity to the lighting assembly.

Another problem with metal heat sinks is that the thermal pathway fromthe LED to the metal heat sink is of limited area. If the LED is mountedby mounting leads, the thermal pathway may be limited to the area of theleads. In some lighting assemblies, a thermally conductive underfillmaterial is disposed between the LED and the metal core printed circuitboard to facilitate heat transfer. Such underfilling, especially whenused in conjunction with an LED having an integral heat slug,substantially increases the thermal pathway area, but generally cannotincrease the thermal pathway area substantially beyond the overallfootprint area of the LED.

In some other approaches, the LEDs are potted using a thermallyconductive material. For example, Roney et al., U.S. Pat. No. 5,632,551and Roney et al., U.S. Pat. No. 5,528,474 disclose potted LEDassemblies. Typically, the potting material is a two-component epoxy orother two-component potting material that is combined or mixed as it isapplied to the lighting assembly, and is then cured. Polycondensation,addition reactions, or other chemical processes occurring in the mixtureduring curing causes solidification of the potting material around theLEDs of the lighting assembly.

Potting can provide a larger thermal contact area between the LED andthe heat sink, but has certain other disadvantages. A container orhousing is typically required to retain the potting material in itsliquid form during solidification. The container or housing adds weightand bulk to the lighting assembly, and may be problematic for certainlow-profile lighting assemblies. Moreover, the potting materialtypically does not have enough thermal mass by itself to dissipate heatgenerated by the LEDs. Accordingly, potting is commonly employed inLED-based lighting assemblies in conjunction with a metal heat sink.

The following contemplates improved apparatuses and methods thatovercome the above-mentioned limitations and others.

BRIEF SUMMARY

According to one aspect, a lighting assembly is disclosed, including aprinted circuit board and one or more light emitting diode diodes (LEDs)disposed on the printed circuit board and connectable with a powersource via circuitry of the printed circuit board. A thermoplasticovermolding covers at least portions of the printed circuit boardproximate to the one or more LEDs. The thermoplastic of thethermoplastic overmolding has a melting temperature greater than about100° C. and has a thermal conductivity greater than or about 1 W/m·K.

According to another aspect, a method of manufacturing a lightingassembly is disclosed. One or more light emitting diode diodes (LEDs)are attached to a printed circuit board. The attached LEDs areconnectable with a power source via circuitry of the printed circuitboard. An overmolding material is insert molded an over at leastportions of the printed circuit board proximate to the LEDs. Theovermolding material has a melting temperature greater than about 100°C. and has a thermal conductivity greater than or about 1 W/·K.

According to another aspect, a method of manufacturing a lightingassembly is disclosed. One or more light emitting diode diodes (LEDs)are attached to a printed circuit board. The attached one or more LEDsare connectable with a power source via circuitry of the printed circuitboard. A thermoplastic is reflowed over at least portions of the printedcircuit board proximate to the one or more LEDs. The thermoplastic has amelting temperature greater than about 100° C. and has a thermalconductivity greater than or about 1 W/m·K.

According to another aspect, a lighting assembly is disclosed, includinga printed circuit board and a plurality of light emitting diode diodes(LEDs) disposed on the printed circuit board and connectable with apower source via circuitry of the printed circuit board. A free standinghigh thermal conductivity material overmolding covers at least portionsof the printed circuit board proximate to the LEDs. The free standinghigh thermal conductivity material has a melting temperature greaterthan about 100° C. and has a thermal conductivity greater than or about1 W/m·K.

Numerous advantages and benefits of the present invention will becomeapparent to those of ordinary skill in the art upon reading andunderstanding the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various process operations and arrangements ofprocess operations. The drawings are only for purposes of illustratingpreferred embodiments and are not to be construed as limiting theinvention.

FIG. 1 diagrammatically shows a lighting assembly including LEDs andfree-standing high thermal conductivity material overmolding on bothfront and back principal sides of a supporting printed circuit board.

FIGS. 2A, 2B, and 2C diagrammatically show an insert injection moldingprocess for forming the free-standing high thermal conductivity materialovermolding of the lighting assembly of FIG. 1. FIG. 2A diagrammaticallyshows the printed circuit board with LEDs attached, arranged betweenmating components of an insert injection mold. FIG. 2B diagrammaticallyshows the lighting assembly inside the mating components of the insertmold, but before injection of the melted thermoplastic. FIG. 2Cdiagrammatically shows the lighting assembly inside the matingcomponents of the insert mold after injection of the meltedthermoplastic.

FIG. 3 diagrammatically shows a lighting assembly similar to that ofFIG. 2, but including the free-standing high thermal conductivitymaterial overmolding on only one side of the printed circuit board.

FIG. 4 diagrammatically shows a lighting assembly similar to that ofFIG. 2, but in which the printed circuit board is a metal-core printedcircuit board.

FIG. 5 diagrammatically shows a lighting assembly similar to that ofFIG. 2, but in which the light emitting diodes (LEDs) are covered by adome-shaped light-transmissive cover.

FIG. 6 diagrammatically shows a portion of an LED-based lighting stringincluding spaced-apart lighting assembly modules attached to a flexibleelectrical cable by insulation-displacing connectors.

FIG. 7 diagrammatically shows a perspective view of one of the lightingassembly modules of the LED-based lighting string of FIG. 6. Thelighting assembly module includes free-standing high thermalconductivity material overmolding, and insulation-displacing connectorsfor connecting with the flexible electrical cable.

FIG. 8 diagrammatically shows an overhead view of an illuminated channelletter that is illuminated by the lighting string of FIG. 6 disposedinside of the channel letter housing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, a lighting assembly 8 includes a printedcircuit board 10 on which one or more light emitting diodes (LEDs) 12are attached. In the illustrated embodiment, three LEDs are attached tothe printed circuit board, however, the number of attached LEDs can beone, two, three, four, or more. Substantially any type of LED can beattached, such as for example: a white LED including an ultravioletgroup III-nitride-based electroluminescent semiconductor diode coated bya white-light emitting phosphor blend; a white LED including a blue orviolet group III-nitride-based electroluminescent semiconductor diodecoated by a yellowish-light emitting phosphor blend; a blue LEDincluding a blue group III-nitride-based electroluminescentsemiconductor diode; a red LED including a red group III-arsenide, groupIII-phosphide, or group III-arsenide-phosphide electroluminescentsemiconductor diode; a red LED including a red group III-arsenide, groupIII-phosphide, or group III-arsenide-phosphide laser diode; an organicelectroluminescent light emitting diode; or so forth. In the illustratedembodiment, each LED 12 includes a base 14 containing anelectroluminescent semiconductor chip and an optional heat slug(internal components not shown), and a light emitting aperture includinga lens 16. Suitable LEDs include, for example, Luxeon® emitters(available from LumiLeds Lighting, LLC, San Jose, Calif.).

The printed circuit board 10 includes printed circuitry (not shown)connecting the one or more LEDs 12 with a suitable power input such asillustrated electrical pads 20 disposed on the printed circuit board 10,or a power receptacle disposed on or connected with the printed circuitboard, or so forth. Optionally, the lighting assembly 8 includes otherelectrical or electronic components such as an illustrated powerconditioning integrated circuit 22, a current-limiting resistor, anelectrostatic discharge protection device, or so forth. In theillustrated lighting assembly 8, the LEDs 12 and other components 22 aredisposed on a single principal side of the printed circuit board 10;however, in other embodiments components may be disposed on bothprincipal sides of the printed circuit board and electricallyinterconnected by suitable through-hole vias, wrap-around printedcircuitry, or so forth.

The LEDs 12 can be attached to the printed circuit board 10 in anysuitable manner, such as soldering to bonding pads of the printedcircuitry, insertion into a suitable socket adapted to receive the leadsof the LED, or so forth. If the LED includes an integral heat slug, thismay be separately soldered or attached to the printed circuit board by asuitable underfill material. In some LED designs, the slug is notelectrically neutral, in which case the slug attachment should beelectrically isolated from the attachments of the LED leads. CommercialLEDs typically have suitable manufacturer-specified attachment methodsor procedures. While surface-mount LEDs are advantageous, it is alsocontemplated to employ wire-bonded LEDs with suitable wire bondelectrical connections. The additional components 22 can be similarlyattached by suitable methods, such as insertion into a suitably adaptedsocket, soldering, wire bonding, or so forth.

The printed circuit board 10 of the lighting assembly 8 shown in FIG. 1does not include a metal core or other metal heat sink. Rather, afront-side free-standing high thermal conductivity material overmolding30 and a backside free-standing high thermal conductivity materialovermolding 32 are disposed on the front and back principal sides,respectively, of the printed circuit board 10. In some embodiments, thefree-standing high thermal conductivity material used for theovermolding 30, 32 is a thermally conductive thermoplastic material or athermally conductive thermoset material. In some embodiments, thefree-standing high thermal conductivity material used for theovermolding 30, 32 is a Therma-Tech™ liquid crystalline polymer,thermally conductive and electrically insulating thermoplastic material(available from PolyOne Corporation, Avon Lake, Ohio). Therma-Tech™thermally conductive thermoplastic is available with thermalconductivity values of between greater than about 1 W/m·K (e.g.,electrically insulating Therma-Tech™ LC5000C TC has thermal conductivityof about 2-3 W/m·K), and greater than about 10 W/m·K (e.g., electricallyconductive Therma-Tech™ SF-4500 TC and LC-6000 TC have thermalconductivities of 10.90 W/m·K and 18-20 W/m·K, respectively). If anelectrically conducting high thermal conductivity material is used, thenany printed circuitry, LED leads, or other exposed conductors aresuitably coated with an insulative dielectric before disposing theelectrically and thermally conductive high thermal conductivitymaterial. On the other hand, electrically insulating high thermalconductivity material such as Therma-Tech™ LC5000C TC can be disposedonto conductors without an intervening insulative layer.

With reference to FIGS. 2A, 2B, and 2C, in some embodiments thefree-standing high thermal conductivity material overmolding 30, 32 areformed simultaneously by insert molding. The resulting overmoldings 30,32 are free-standing after removal from the insert mold. As shown inFIG. 2A, the printed circuit board 10 with LEDs 12 and other components22 attached is disposed between mating components 40, 42 of an insertmold. FIG. 2B shows the two mating mold components 40, 42 after matingto form the closed insert mold having a cavity containing the printedcircuit board 10 with LEDs 12 and other components 22 attached. The moldcomponent 40 is designed with molding regions 44 for forming thefront-side overmold 30, and optional isolation regions 46 that receivethe LEDs 12 to prevent at least the light output apertures of the LEDs12 including the lenses 16 from being covered by the overmolding. Insome embodiments, the isolation regions define gaps between the LEDs 12and the frontside overmolding 30. In the illustrated lighting assembly8, the isolation regions 46 allow the frontside overmolding 30 toapproximately abut the bases 14 of the LEDs 12. In some embodiments, theisolation regions allow the frontside overmolding 30 to overcoat aportion of the base 14. If the high thermal conductivity material of theovermolding 30 is sufficiently optically transmissive, it is alsocontemplated to omit the isolation regions 46 and allow the front-sideovermolding 30 to cover the lenses 16 of the LEDs 12. The mating insertmold component 42 includes a molding region 48 for forming the backsideovermold 32.

With reference to FIG. 2C, the thermally conductive thermoplastic orother high thermal conductivity molding material is typically suppliedin pellets or other solid pieces (not shown) that are heated to formmolten molding material that is delivered under pressure to the cavityby delivery conduits 52, such as a sprue and runners delivery system.Injected melted high thermal conductivity molding material 56 fills themolding regions 44, 48 where it solidifies to define the front-side andbackside high thermal conductivity material overmoldings 30, 32. Themold 40, 42 is then opened and the lighting assembly 8 is removed.Optionally, flash or other molding artifacts are trimmed off.

The insert molding process described with example reference to FIGS. 2A,2B, and 2C is an illustrative example. Substantially any insert moldingprocess can be employed to form the high thermal conductivity materialovermoldings 30, 32. Because the lighting assembly 8 is removed from themold 40, 42 after completion of the insert injection molding process,the lighting assembly 8 suitably does not include a container or housingconfigured to contain the thermoplastic or other high thermalconductivity overmoldings 30, 32. Rather, the high thermal conductivityovermoldings 30, 32 are free standing, enabling the lighting assembly 8to have a low profile.

With reference to FIG. 3, a lighting assembly 8′ is similar to thelighting assembly 8 of FIG. 1, except that the backside free-standinghigh thermal conductivity material overmolding 32 is omitted. Omissionof the backside free-standing high thermal conductivity materialovermolding 32 can simplify the insert molding or other overmoldingprocessing, and can make it easier to mount the lighting assembly.However, including the backside free-standing high thermal conductivitymaterial overmolding 32 improves heat transfer to the surroundingambient.

With reference to FIG. 4, a lighting assembly 8″ is similar to thelighting assembly 8 of FIG. 1, except that the printed circuit board 10is replaced by a metal core printed circuit board 10″, and the two highthermal conductivity material overmoldings 30, 32 are connected by anovermolding portion 60 extending across the front and back principalsurfaces of the printed circuit board 10″ to define a single continuousthermally conductive overmolding 30, 32, 60. The metal core printedcircuit board 10″ includes a thin dielectric layer 62 disposed on ametal sheet or plate defining the metal core 64. The thin dielectriclayer 62 is preferably thin to enable good thermal conduction betweenthe LEDs 12 and other components 22 and the metal core 64. Thecombination of the thermally conductive overmolding 30, 32, 60 and metalcore 64 can provide enhanced heat dissipation versus a lighting assemblywith either the overmolding or the metal core alone. However, the metalcore 64 is typically made of copper or another high density metal thatadds substantial weight to the lighting assembly 8″.

With reference to FIG. 5, a lighting assembly 88 is similar to thelighting assembly 8 of FIG. 1, except that the LEDs 12 are enclosed in alight-transmissive cover such as the illustrated example dome-shapedcover 90 that has its base secured to the printed circuit board 10.Optionally, the light-transmissive cover 90 includes one or more opticalcoatings 92 (diagrammatically indicated by a dashed line in FIG. 5),such as a phosphor coating, an ultraviolet reflector, or so forth. Somesuitable light transmissive cover configurations that enhance lightoutput, provide efficient ultraviolet-to-visible phosphor conversion,protect the LEDs from damaging physical contact, or provide otheradvantages are disclosed in Aanegola et al., U.S. Publ. Appl.2005/0239227 A1. A modified front-side free-standing high thermalconductivity material overmolding 130 does not fully cover thelight-transmissive cover 90, but rather contacts only the base regionnear where the light-transmissive cover 90 is secured to the printedcircuit board 10.

With reference to FIGS. 6 and 7, the disclosed heat management conceptsare readily applied to LED-based lighting strings. FIG. 7 illustrates aportion of an example lighting string 180 that includes a plurality oflighting assembly modules 188 connected to an insulated flexibleelectrical cable 190 by insulation displacing connectors 192, 194. Theflexible electrical cable 190 includes a plurality of flexibleconductors 196, 198 and insulation 200 (indicated diagrammatically inFIG. 6 by dashed lines) surrounding the flexible conductors 196, 198.The insulation displacing connectors 192, 194 displace the cableinsulation 200 and electrically connect with the flexible conductors196, 198. In other contemplated embodiments, the flexible electricalcable 190 is replaced by a cable having three or more conductorsincluding one or more series conductors for enabling series-parallelinterconnection of lighting assembly modules. In other contemplatedembodiments, the continuous cable 190 is replaced by short flexibleconductor lengths disposed between and electrically connectingneighboring lighting assembly modules.

With particular reference to FIG. 7, each lighting assembly module 188includes a printed circuit board 210 supporting an LED 212 including abase 214 containing an electroluminescent semiconductor chip and anoptional heat slug (internal components not shown), and a light emittingaperture including a lens 216. Suitable LEDs include, for example,Luxeon® emitters (available from LumiLeds Lighting, LLC, San Jose,Calif.). The insulation displacing connectors 192, 194 are soldered orotherwise electrically connected with electrical pads 220 to deliverelectrical power from the flexible conductors 196, 198 of the cable 190to the printed circuit board 210 and thence to the LED 212 via printedcircuitry of the printed circuit board 210. Optionally, each lightingassembly module 188 includes other electrical or electronic componentssuch as an illustrated power conditioning integrated circuit 222, acurrent-limiting resistor, an electrostatic discharge protection device,or so forth. In the illustrated lighting assembly module 188, the LEDs212 and other components 222 are disposed on a single principal side ofthe printed circuit board 210; however, in other embodiments componentsmay be disposed on both principal sides of the printed circuit board andelectrically interconnected by suitable through-hole vias, wrap-aroundprinted circuitry, or so forth.

A free-standing thermoplastic or other high thermal conductivitymaterial overmolding 230 (indicated diagrammatically by dotted lines inFIGS. 6 and 7) is disposed over the entire printed circuit board 210 andcomponents 212, 222 disposed thereon, except that an opening 234 isprovided through which the light output aperture lens 216 and a portionof the base 214 of the LED 212 protrudes. The illustrated free-standingthermoplastic or other high thermal conductivity material overmolding230 also extends beyond the edges of the printed circuit board 210 toconnect the overmoldings on the front and back principal sides of theprinted circuit board 210 to define a continuous overmolding. Theillustrated free-standing thermoplastic or other high thermalconductivity material overmolding 230 also covers ends of theinsulation-displacing connectors 192, 194 in the vicinity of theelectrical pads 220 of the printed circuit board. Thus, thefree-standing thermoplastic or other high thermal conductivity materialovermolding 230 provides thermal dissipation for heat generated at thejunction between the insulation-displacing connectors 192, 194 and theelectrical pads 220.

With reference to FIG. 8, an example application of the LED-basedlighting string of FIG. 6 is shown. An illuminated channel letter 250includes the lighting string 180 disposed inside of a channel letterhousing 252. The example illustrated channel letter housing 252represents the capital letter “D”; however, channel letter housingsrepresenting other capital letters, or lower case letters, or numerals,or other symbols, or images, logos, or so forth, can also be used. Inthe illustrated embodiment, the lighting string 180 is disposed on abottom inside surface of the channel letter housing 252, and is suitablysecured by cable clamps, adhesive, or so forth (securing not shown inFIG. 8). In other embodiments, the lighting string may be disposed on aninner sidewall of the channel letter. Typically, the channel letterhousing 252 includes a light transmissive top cover (not visible in theoverhead view of FIG. 8 due to its transparency). The light transmissivetop cover may be colored or clear, and is optionally translucent orpartially reflective to provide some light scattering.

In each of the lighting assemblies 8, 8′, 8″, 88 and lighting assemblymodules 188, the free-standing thermoplastic or other high thermalconductivity material overmolding 30, 32, 60, 130, 230 provides alightweight and efficient thermal dissipation pathway for transferringheat produced by the LEDs 12, 212 and optional other components 22, 222to the external ambient and/or to a thermally conductive mountingsurface on which the lighting assembly is disposed. Because the LEDs 12,212 are preferably high-brightness LEDs that typically operate attemperatures close to 100° C., the free-standing thermoplastic or otherhigh thermal conductivity material overmolding 30, 32, 60, 130, 230should have a melting temperature greater than about 100° C. to ensurethat the thermoplastic does not melt during operation of the lightingassembly. If the high thermal conductivity material of the overmolding30, 32, 60, 130, 230 is a thermoset material, then the thermosetmaterial should be thermally stable at up to about 100° C. after thethermosetting process is completed.

At the same time, the LEDs 12, 212 and optional other components 22,222, or features associated therewith such as phosphor coatings, solder,thermosonic, or other bonds, or so forth, are typicallytemperature-sensitive. Since the overmolding is typically performedafter attachment of these temperature-sensitive components, theovermolding process should not expose these components to excessivetemperature. If insert injection molding is used to apply theovermolding 30, 32, 60, 130, 230, then the melted overmolding materialin the insert mold should be at a temperature of greater than about 100°C. (in order to be melted, that is, in a liquid or other low viscosityphase) and at a temperature less than a damage temperature threshold forelements of the lighting assembly. The damage temperature threshold isdetermined by the lowest temperature that will damage a heat-sensitiveelement of lighting assembly. Depending upon the temperature-limitingelement, this upper temperature bound is typically a few hundred degreesCelsius to about 500° C. or higher in some embodiments.

Thermally conductive thermoplastics, such as the example Therma-Tech™thermoplastic which melts at between 310° C. and 350° C., areadvantageous for use as the high thermal conductivity material of theovermolding 30, 32, 60, 130, 230 because these melting temperatures arehigh enough to avoid reflow of the thermoplastic at LED operatingtemperatures, but low enough to enable injection molding or otherformation of the high thermal conductivity overmolding 30, 32, 60, 130,230 without damaging temperature-sensitive elements of the lightingassembly. Because thermoplastics do not require heating to induce athermosetting chemical reaction, thermoplastics are melted to performinsert injection molding without a concomitant chemical reaction, and sothe melting temperature of thermoplastics is typically relatively low.

In contrast, thermosetting materials tend to be brought to a highertemperature in the insert mold so as to thermally drive polymericcross-linking or other thermosetting chemical reactions. However, athermally conductive thermoset material can also be used for the highthermal conductivity material overmolding 30, 32, 60, 130, 230 if thethermosetting temperature is below the damage temperature threshold forthe lighting assembly.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

The invention claimed is:
 1. A lighting assembly comprising: a pluralityof lighting assembly modules each including a printed circuit board, oneor more light emitting diodes (LEDs) disposed on the printed circuitboard and connectable with electrical connectors disposed with theprinted circuit board via circuitry of the printed circuit board, and afree-standing high thermal conductivity material overmolding that coversat least portions of the printed circuit board proximate to the one ormore LEDs, the free-standing high thermal conductivity material having amelting temperature greater than about 100° C. and having a thermalconductivity greater than or about 1 W/m·K; and flexible electricalconductors interconnecting the lighting assembly modules via theelectrical connectors to define a flexible LED-based lighting string. 2.The lighting assembly as set forth in claim 1, wherein the circuitboards do not include metal cores.
 3. The lighting assembly as set forthin claim 1, wherein the free-standing high thermal conductivity materialof the overmolding is a thermoplastic material or a thermoset material.4. The lighting assembly as set forth in claim 1, wherein thefree-standing high thermal conductivity material overmolding has a shapecomporting with molding regions defined by an insert mold that isconfigured to receive the printed circuit board with the one or moreLEDs disposed thereon.
 5. The lighting assembly as set forth in claim 1,wherein each lighting assembly module includes one or more lensescorresponding to and disposed over the one or more LEDs disposed on theprinted circuit board, and the free-standing high thermal conductivitymaterial overmolding does not cover at least a portion of each of theone or more lenses.
 6. A lighting assembly comprising: a plurality ofLEDs; a plurality of spaced-apart printed circuit boards, the pluralityof LEDs being disposed on the spaced-apart printed circuit boards; aplurality of thermoplastic overmoldings corresponding to the pluralityof printed circuit boards, the thermoplastic overmoldings covering atleast portions of the corresponding printed circuit boards proximate tothe LEDs disposed on the printed circuit boards, the thermoplastic ofthe thermoplastic overmoldings having a melting temperature greater thanabout 100° C. and having a thermal conductivity greater than or about 1W/m·K; a flexible electrical cable including a plurality of flexibleconductors and insulation surrounding the flexible conductors; and aplurality of insulation-displacing conductors electrically connectedwith and secured to each printed circuit board, the plurality ofinsulation-displacing conductors displacing the cable insulation andelectrically connecting with flexible conductors so that the pluralityof LEDs disposed on the plurality of printed circuit boards areconnectable with a power source via circuitry of the printed circuitboards, the insulation-displacing conductors, and the flexibleconductors of the flexible electrical cable.
 7. The lighting assembly asset forth in claim 6, wherein the thermoplastic overmolding of eachprinted circuit board covers ends of the insulation-displacingconnectors secured to the printed circuit board.
 8. The lightingassembly as set forth in claim 6, wherein the lighting assembly furthercomprises: a channel letter housing, the plurality of spaced-apartprinted circuit boards and at least a portion of the flexible electricalcable being disposed inside the channel letter housing.
 9. The lightingassembly as set forth in claim 6, wherein the thermoplastic of thethermoplastic overmoldings has a thermal conductivity greater than orabout 10 W/m·K.
 10. The lighting assembly as set forth in claim 6,wherein the circuit boards do not include metal cores.
 11. The lightingassembly as set forth in claim 6, wherein the thermoplastic overmoldingsapproximately abut or contact the bases of the LEDs but do not coverlight-emitting apertures of the LEDs.
 12. The lighting assembly as setforth in claim 6, wherein the thermoplastic overmoldings substantiallycover both principal sides of the printed circuit boards.
 13. Thelighting assembly as set forth in claim 6, wherein the thermoplasticovermoldings have a shape comporting with molding regions defined by aninsert mold that is configured to receive the printed circuit boardswith the LEDs disposed thereon.
 14. The lighting assembly as set forthin claim 6, further comprising: light-transmissive covers disposed overthe LEDs, the thermoplastic overmoldings not covering at least a portionof each light-transmissive cover.
 15. The lighting assembly as set forthin claim 14, wherein the light-transmissive covers are lenses disposedover the LEDs.